Java如何自定义线程池(ThreadPoolExecutor)呢?

自定义线程池的方法

Java通过Executors提供四种线程池:
    newCachedThreadPool:
	   创建一个可缓存线程池
       当线程池长度超过处理需要,可灵活回收空闲线程
	   当无可回收,则新建线程(线程最大并发数不可控制)
newFixedThreadPool:
       创建一个定长线程池,可控制线程最大并发数,超出的线程会在队列中等待
newScheduledThreadPool:
       创建一个定长线程池,
	    支持定时及周期性任务执行
newSingleThreadExecutor:
       创建一个单线程化的线程池,
	    它只会用唯一的工作线程来执行任务,
		 保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行

Executors创建四种线程的源码

1.newFixedThreadPool
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>(),
                                      threadFactory);
    }
 
2.newCachedThreadPool
public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }
 
3.newSingleThreadExecutor
public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }
 
4.newScheduledThreadPool
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

public ScheduledThreadPoolExecutor(int corePoolSize) {
        super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS,
              new DelayedWorkQueue());
    }

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }
 

ThreadPoolExecutor构造方法

public ThreadPoolExecutor(int corePoolSize,//核心线程池大小
                              int maximumPoolSize,//最大线程池大小
                              long keepAliveTime,//线程池中超过corePoolSize数目的空闲线程最大存活时间；可以allowCoreThreadTimeOut(true)成为核心线程的有效时间
                              TimeUnit unit,//keepAliveTime的时间单位
                              BlockingQueue<Runnable> workQueue,//阻塞任务队列
                              ThreadFactory threadFactory,//线程工厂:用于创建线程
                              RejectedExecutionHandler handler) {//拒绝策略:当提交任务数超过maxmumPoolSize+workQueue之和时，任务会交给RejectedExecutionHandler来处理
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

注意事项:
1.当线程池小于corePoolSize时，新提交任务将创建一个新线程执行任务，即使此时线程池中存在空闲线程。
2.当线程池达到corePoolSize时，新提交任务将被放入workQueue中，等待线程池中任务调度执行
3.当workQueue已满，且maximumPoolSize>corePoolSize时，新提交任务会创建新线程执行任务
4.当提交任务数超过maximumPoolSize时，新提交任务由RejectedExecutionHandler处理
5.当线程池中超过corePoolSize线程，空闲时间达到keepAliveTime时，关闭空闲线程
6.当设置allowCoreThreadTimeOut(true)时，线程池中corePoolSize线程空闲时间达到keepAliveTime也将关闭
7.RejectedExecutionHandler接口有四个实现类(四种拒绝策略）
	(1).AbortPolicy：抛出RejectedExecutionException异常；
	(2).CallerRunsPolicy：它直接在 execute 方法的调用线程中运行被拒绝的任务；如果执行程序已关闭，则会丢弃该任务
	(3).DiscardPolicy：不能执行的任务将被删除;
	(4).DiscardOldestPolicy:位于工作队列头部的任务将被删除(如果失败，会重复执行)
8.默认的拒绝策略
   /**
     * The default rejected execution handler
     */
   private static final RejectedExecutionHandler defaultHandler =
      new AbortPolicy();

自定义线程池:单例

public class AsynTaskThreadPool {

    private int corePoolSize = 2;
    private int maxinumPoolSize = 10;
    private long keepAliveTime = 1000L;
    private TimeUnit unit = TimeUnit.SECONDS;
    private int capacity = 10;
    private BlockingQueue<Runnable> workQueue = null;
    private ThreadFactory threadFactory = null;
    private RejectedExecutionHandler handler = new ThreadPoolExecutor.AbortPolicy();
    private ThreadPoolExecutor        exeThreadPool      = null;
    private static AsynTaskThreadPool   asynTaskThreadPool = null;
    private AsynTaskThreadPool(int corePoolSize,int maxinumPoolSize,String namePrefix, int timeoutQueueSize){
        this.corePoolSize = corePoolSize > 0 ? corePoolSize : this.corePoolSize;
        this.maxinumPoolSize = maxinumPoolSize > 0 ? maxinumPoolSize : this.maxinumPoolSize;
        //线程安全的队列
        workQueue = new ArrayBlockingQueue<>(timeoutQueueSize > 0 ? timeoutQueueSize : this.capacity);
        exeThreadPool = new ThreadPoolExecutor(corePoolSize, maxinumPoolSize, timeoutQueueSize, unit, workQueue, threadFactory, handler);
    }

    public void execute(Runnable task){
        exeThreadPool.submit(task);
    }

    public <T> Future<T> execute(Callable<T> task){
        return exeThreadPool.submit(task);
    }

    public static AsynTaskThreadPool getInstance(int corePoolSize, int maximumPoolSize, String namePrefix,
            int timeoutQueueSize){
        asynTaskThreadPool = new AsynTaskThreadPool(corePoolSize,maximumPoolSize,namePrefix,timeoutQueueSize);
        return asynTaskThreadPool;
    }

    static class AsynTaskThreadFactory implements ThreadFactory{
        private final AtomicInteger threadNum = new AtomicInteger(0);
        private String threadName = "";
        @Override
        public Thread newThread(Runnable r) {
            Thread th = new Thread(r,threadName+threadNum.getAndIncrement());
            //设置为用户线程(默认是false,为用户线程)
            th.setDaemon(false);
            return th;
        }
    }

    /**
     * 关闭线程池
     */
    public void shutDown() {
        exeThreadPool.shutdown();
    }

    public int getCorePoolSize() {
        return corePoolSize;
    }

    public int getMaxinumPoolSize() {
        return maxinumPoolSize;
    }

    public long getKeepAliveTime() {
        return keepAliveTime;
    }
}